1. Field of the Invention
This invention relates to apparatus for forming a fluid-tight seal between confronting surfaces; more particularly, to a surface-mounted gasket having dual sealing members.
2. Description of the Prior Art
Providing a reliable, durable seal between an opening in a pressure vessel and its closure has posed a continuing challenge to workers in the art despite the many inovations in materials for use in sealing devices. In a sterilizer, for example, which may operate under both positive and negative pressures during a given sterilization cycle, there exists the problem of providing an effective seal between the sterilizer door and the door frame under conditions of high door usage.
Sealing gaskets for sterilizer doors, whether mounted on the door or on the frame, traditionally have been held in place by means of gasket bars, which extend around the perimeter of the opening to be sealed and involve the application of considerable labor during installation and removal of a gasket, or precisely machined grooves in one of the surfaces to be sealed. The latter hold the base of the gasket in place and require close tolerances with the gasket dimensions to be effective.
A further problem associated with sealing gaskets for sterilizer doors is the tendency of the gasket material to acquire permanent deformation (or set) after being repeatedly crushed between the surfaces to be sealed. This problem is most critical when a compression-type sealing gasket is employed because a certain amount of compressive force on the gasket is necessary to effect a seal. When excessive compression is applied, principally by the sealing surfaces being brought too closely together for the particular gasket present, there is a drastic reduction in the life of the gasket due to the permanent deformation or set.
When a lip seal gasket is employed, crushing of the seal is not essential to its operation because the seal depends for its effectiveness on the presence of a pressure differential across the lip. Nevertheless, undue crushing of a lip seal can cause permanent deformation of the flexible lips and a resultant decrease in seal life. As with compression seals, the maintenance of proper spacing between the surfaces to be sealed by a lip seal is vital to its operation.
In general, neither gasket bars nor grooves as mounting means for sterilizer door sealing gaskets address the problem of providing repeatable proper spacing between the surfaces to be sealed with each door closing.